822 MAJOR G. E. H. BARRETT-HAMILTON AND 



to catch during the summer months, further investigation of the 



islands was then postponed. 



Among those who have assisted the work of exploration, either 



financially or with local assistance, we may specially mention 



the Duke' of Argyll, the Marquis of Bute, Mr. A. R. Macgregor, 

 Mrs. Hugh Morrison of Islay, Mr. Colin Campbell of Jura, and 



Mr. Harold Russell. 



The present collection has come well up to expectations, since 



it has resulted in the discovery of three quite distinct forms 

 belonging to the genera Sorex, Evotomys, and Microtus'* . 



In working out the fauna of small islands, two distinct phe- 

 nomena mvist be disentangled. A peculiar mammal found on 

 a small island may represent a new development under insular 

 conditions, it may represent the survival of an ancient type else- 

 wdiere extinct, and, as is often the case, it may combine both 

 features. We believe that Sorex grantii is an entirely new de- 

 velopment, and that Evotomys (ilstoni and Mierotus agrestis mac- 

 gillivraii are instances of " relics " surviving with little alteration 

 from the pleistocene epoch. The meaning of these three forms 

 has been partly discussed under the description of each of them ; 

 but it would be premature to enter upon an extended discussion of 

 the cause of variation or survival in islands. The influence of a 

 comparatively recent glacial period, and the extermination brought 

 about by man, now proved to be an ancient inhabitant of Britain, 

 are difficult to follow ; and at all periods the British Islands have 

 been the scene of constantly shifting environments and altering 

 or variable climates, due princijjally to the proximity of a great 

 ocean and the frequent oscillations of sea-level. Many of our 

 common genera of mammals have inhabited the British Islands 

 since the deposition of the late pliocene Forest-Bed, but no one 

 has as yet ventured to guess how often they may have been 

 exterminated, to return again in fresh vigour on the resumption 

 of favourable conditions. The history of the British fauna 

 resolves itself into that of the various invasions or "migrations" 

 of mammals, which have been no less real, albeit more ancient 

 and more difficult to trace, than those of Kelt, Roman, Saxon, 

 Skandinavian, and Norman. The seveiity of the struggle for 

 existence has in our area undergone profound variation, accord- 

 ing as the sea cut off" or united our area with Europe, according 

 as severe climatic conditions were combined with insularity or 

 connection with the Continent. But, however frequently the 

 faima may have been exterminated, renewed junctions with 

 the mainland have from time to time refi'eshed it with new 

 stock, and the geological records of what seem from a distance 

 almost kaleidoscopic changes are only now in process of 

 disentanglement. 



* [The complete account of these new forms appear here, but since the names and 

 preliminar}- diagnoses were published in the 'Abstract,' No. 119, 1913, they are 

 distinguished by being underlined. — Editor.] 



